The invention relates to an electrical contacting system for an electrophoretic dip painting plant for motor vehicle bodies, with which the bodies are guided through an electrophoretic dip paint bath by means of an overhead conveyor. The bodies are thereby each arranged on a body carrier and connected to this in an adequately secure manner; the body carrier is a flat structure which is approximately rectangular in the plan view, is customarily designated as a slide or skid and often has the shape of a rectangular carrier frame. The overhead conveyor possesses a plurality of conveyor hangers which are arranged one behind the other in the direction of conveyance and in spaced relation to one another and which are suspended so as to be pivotable about upper pivot axes extending horizontally and transversely to the direction of conveyance and are designed such that two conveyor hangers following one another in the direction of conveyance can engage beneath a respective body carrier in its front and in its rear area, respectively, and support it; normally, the conveyor hangers have the shape of a rectangular frame with a lower crossbar for engaging beneath a body carrier, wherein the plane of the frame normally extends vertically.
In the case of the electrophoretic dip paint bath, this is an aqueous suspension, from which color particles are deposited on the body submerged in the paint bath by way of electrophoresis when a corresponding, electrical difference in potential is maintained between the paint bath and the body. For this purpose, the bodies are connected in an electrically conductive manner to the metal body carriers and a corresponding electrical potential is applied to the conveyor hangers via the overhead conveyor; in addition, not only the conveyor hangers but also the body carriers are provided with electrical contacting devices which provide an electrical connection between conveyor hanger and body carrier when the latter is placed on two conveyor hangers. Moreover, these contacting devices also have the task of preventing any floating up of a body and thus any lifting of the body carrier from the two conveyor hangers supporting it when the overhead conveyor submerges the body in the paint bath--even if the body of a passenger vehicle is submerged in the paint bath with an open trunk lid, the trunk may, in the case of certain body shapes, not be filled by the aqueous suspension forming the paint bath until the load sill of the trunk dips into the paint bath and so without any locking of the body carrier to the conveyor hangers the trunk still filled with air would lead to the body carrier lifting away, in particular, from the conveyor hanger adjacent to the trunk.
DE-40 41 211-C1 discloses an electrophoretic dip painting plant of the type described above. In the known construction, the conveyor hangers have the shape of rectangular frames with a plane of the frame normally extending vertically and the body carriers have the shape of rectangular frames with a plane of the frames extending horizontally over the greatest portion of the path of conveyance. Two lower contacting devices are secured to the lower crossbar of each conveyor hanger and these consist essentially of a support and contact pin projecting vertically upwards and a rail-like guide element arranged next to the pin transversely to the direction of conveyance and likewise projecting vertically upwards. Two upper contacting devices are secured to each of the two longitudinal frame legs of the body carrier, namely one in the front and one in the rear area of the body carrier; each of these contacting devices has a metal protective bell which is open to the bottom, may be placed from above onto the support and contact pin of one of the lower contacting devices and encloses and stores a bubble of air when it dips into the paint bath from above. The protective bell has two side walls and a circular cylindrical circumferential wall which connects these side walls to one another and forms with the inner side of its upper area a support and contact surface, against which the associated support and contact pin abuts when the body carrier is borne by two conveyor hangers. The bubble of air ensures a good electrical contact between the contact surface of the protective bell and the upper end of the support and contact pin--color is applied not only to the body but also to all the areas of the body carrier coming into contact with the paint bath and the upper contacting devices secured to it. Two rib-like locking elements projecting from the side wall of the protective bell facing the guide element of the associated, lower contacting device are secured to this side wall and these locking elements--in a view of this side wall--extend downwards at an angle and towards one another, wherein their lower ends are arranged at a transverse distance from one another so that they form an opening between them, and wherein the angle bisector of the angle formed by the two locking elements extends through the cylinder axis of the circumferential wall of the protective bell.
These two locking elements interact with a locking nose, which is secured to the guide element of the lower contacting device, is approximately of a saw tooth shape in the side view and may be pushed through between the two locking elements from below with a horizontally extending body carrier and vertically extending conveyor hanger, but prevent any lifting of the protective bell from the lower contacting device as soon as--when seen transversely to the direction of conveyance and horizontally--the angle formed by the plane of the frame of the conveyor hanger and the plane of the frame of the body carrier deviates from 90.degree. by more than a specific angle. Since--as is apparent from FIG. 1 of DE-40 41 211-C1--the overhead conveyor submerges the body carriers in the paint bath at an angle and also guides them out of the paint bath again at an angle, wherein the plane of the frame of the guide hangers still extends at least approximately vertically even in this case, such angular deviations occur not only during the submergence of the bodies into the paint bath but also during the guidance of the bodies out of the paint bath.
It has been shown in practice that the construction resulting from DE-40 41 211-C1 cannot ensure a reliable locking of the body carrier on the conveyor hangers, namely during the submergence of the bodies into the paint bath: In this respect, the conveyor hanger adjacent to the trunk of the body and the body carrier can be pivoted relative to one another such that the angle bisector of the V-shaped configuration formed by the two locking elements of a protective bell forms with the plane of the frame of the conveyor hanger a relatively small, acute angle of up to, for example, approximately 12.degree.. This can result in the protective bell disengaging at the lower contacting device when the protective bell moves relative to the support and contact pin of the lower contacting device, during the course of the relative movement between body carrier and conveyor hanger, such that the contact pin does not constantly extend in a plane of diameter of the circular cylindrical circumferential wall of the protective bell. Such a disengaging of protective bells of the body carriers at the lower contacting devices of the conveyor hangers can, however, have extremely disadvantageous consequences--once the bodies are completely submerged in the paint bath, the body carriers are again lowered onto the conveyor hangers, and in this respect protective bells which have previously become disengaged can come to rest adjacent to the associated support and contact pins.